<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
        <div id="app">{{ date }}</div>
        <script src="https://unpkg.com/vue/dist/vue.min.js"></script>
        <script>
           var app = new Vue({
               el:'#app',                          //     {{ }} 的作用
               data:{
                   date:new Date()
               },
               mounted:function (){
                   var  _this = this;
                   this.timer = setInterval(function(){
                       _this.date = new Date();
                   },1000);
               },
               beforeDestroy:function(){
                   if (this.timer){
                       clearInterval(this.timer)
                   }
               }
           })    
        </script>
</body>
</html>